Pituitary-targeted knockout of glucocorticoid receptors disrupts growth hormone expression during embryonic development.

Numerous studies have implicated glucocorticoids in the regulation of somatotroph differentiation. However, few studies have investigated a requirement for glucocorticoid receptors (GR) in this process. We hypothesized that GR is essential for the normal ontogeny of pituitary growth hormone (GH) during mouse embryonic development. Anterior pituitary cells were isolated from e12.5-e13.5 mice and e11 chickens and cultured with or without corticosterone (CORT) in the absence or presence of ZK98299, a GR-specific antagonist. CORT induced GH mRNA expression in pituitary cells from both species, and this response was blocked by inclusion of the GR antagonist. Mouse embryos with pituitary-targeted knockout of GR were generated utilizing the cre-LoxP Recombinase system under control of the pituitary-specific alpha-glycoprotein subunit (αGSU) promoter. All cre-positive GR(-/-) embryos died at birth. Therefore, anterior pituitary, brain, heart, liver, and muscle tissues, were collected on embryonic days 17.5/18.5 for RNA isolation and RT-qPCR analysis. Cre mRNA expression was only found in the pituitary, and GR mRNA levels were significantly decreased in the pituitaries of GR(-/-) embryos. GH mRNA was significantly decreased in pituitary-targeted GR(-/-) knockout embryos in comparison to wild-type GR(+/+) embryos. Significant differences in expression of other pituitary hormones in GR(-/-) embryos were not observed, indicating that the effect of pituitary-targeted knockout of GR was restricted to disruption of GH gene expression. To our knowledge, this is the first report that homozygous GR knockout in the anterior pituitary gland in mice suppresses embryonic GH expression, confirming an essential role for GR signaling in the normal ontogeny of somatotrophs.